We have shown the existence of an as yet unidentified mineralocorticoid in the urine from some patients with low renin hypertension. We propose to extract, purify, and identify this mineralocorticoid utilizing classical techniques of extraction and purification, employing a recently developed mineralocorticoid radioreceptor assay to follow its purification. Once the compound is chromatographically pure, its structure will be identified by physical and chemical techniques. Once this is done a radioimmunoassay will be developed, and the steroid will be measured under a variety of conditions in normal individuals and patients with hypertension.